Utilization of aluminous metal electrodes in cathodic protection installations



Feb. 13, 1951 R. B. HOXENG UTILIZATION OF ALUMINOUS METAL ELECTRODES IN CATHODIC PROTECTION INSTALLATIONS Filed Dec. 26, 1946 l NV ENTOR ficz gg awna' B. hoxeny 6M ATTORN EY Patented Feb. 13, 1951 UNITED STATES PATENT OF'FICET UTi iza'rroN. r ALUMINQUS METALELECF- 'rnonns IN oA noDIc PROTECTION IN- S LLATI Raymond B. Hoxeng, Oakmont, Pa., assignor to Aluminum Company of America, Pittsburgh, Pa a. corporation of Penneylvania.; v

Application December 26, 1946, Serial No. 718,595

9 Glaims... (Cl. zoo-14s) This invention relates to installations designed to cathodicall protect underground metallic structures against corrosion. The invention is specifically directed to installations of this type which utilize, as the anodic metal, aluminum or aluminum alloy having the electrical characteristics of that metal, such alloys usually being those containing upwards of 50 percent by weight of aluminum. Aluminum and such alloys are generally termed aluminous metal andsuch term is used herein and in the appended claims.

The essential elements and the organization of a cathodic protection system or installationarc well known and will only be summarized herein to the endthat the field of the invention Will be clearly defined. Metallic underground structures which may require cathodic protection are of various types, including earth buried linear structures, such as pipe lines for the transport of fluids or gases, and earth buried unit. structures, such as structural tower footings, tanks, oil well casings and the like. In systems designed to cathodically protect such structures against corrosion the metal of the structure is electrically connected, usually by wire or bus, to a separately buried metal piece, called an electrode, which, is

made of metal anodic to the metal oitheunder ground structure. Thus is formed a galvanic cell in which the underground structure is cathode and in which the earth, in which the cell, elements are buried, serves as electrolyte. In com mercial installations of this character it is the object to so fashion the cell that a steadyfiow of current is continuously'produced at high ef ficiency, i. e. at a low rate. of consumption of the metal of the electrode which serves as anode. Where the metallic underground structure is linear or large, if of unit type, a plurality of electrodes is used separately buried at intervals along the structure and may be separately connected thereto. When an electrode, is installed in such a system it is common practice to surroundthe.

buried electrode with a mixture, sometimes called a backfill, which. contains, chemicals which are intended to promote the action of the ,celL-increase its efliciency or otherwise benfifi l the. in-

stallation.

Aluminous metal has properties recommending it for use as electrode in such a cathodic protection system. However, until recently, aluminous metal electrodes have rarely been used in such systems despite the fact that theoretical considerations indicate that aluminous metal, electrodes should deliver more ampere hours per pound thanmost metals available for such use. In-

deed such a cathodic protection cell utilizing aluminum electrodes and operating at percent efficiency is superior, on the basis of ampere hours per pound of metal, to cells utilizing electrodes made of other commercially available metals if such cells could be operated at 100 percent efficiency, This; is evident upon comparison of the electrochemical equivalents of zinc, magnesium and aluminum as shown in the table on page 486 of the Transactionsof the-Electra chemical Society, vol. (19 16), in an article by H. A. Robinson on Magnesium as a Galvanic Anode. Most buried metallic structures are constructed of metal, such as iron or steel, which is cathodic to aluminous metal, yet aluminous ages of corrosion.-

To the end of achieving these and related ob.- jects I improve the action of a cathodic, protection cell embodying-an aluminous metal-anode by providing around the anode a mixture, or baokfill, containing a mercury compound capable of ielding'me-tallic mercurywhen in contact with aluminum. Usually if the backfill mixture contains at least about 0.001 percentby dry weight of thecompound theresults of this invention will: be realized. 1 In-practice I prefer to use 0.05to

1.0 percent by Weight of a relatively-insoluble mercury compound but greater amountsare not harmful and the compounds will give good results even when present in the mixture in very large amounts such as 1-0.0 percent, Results are not improved, however-,- by using excessive amounts, and. economic considerations usually limit the amount used to the smallest amountwhich will be effective under all the circumstances, One factor to be taken into consideration is the sol u bility of the mercury compound. It is usually pre e e tense m rcu ycompounds of limited solubility to insure that the leaching actionoi.

ground waters. or moisture willnot rapidlydeplete the mercury compoundcontent: or. the backfill. mixtur to .a point where. lessthan the desirable.

minimum is present, the occurrence of which inactive toward the aluminous anode, i. e. it may contain as the other components earth, sand, ash, oellulosic material or other substance relatively inert to the electrode. On the other hand, the

mercury compound may be added to backfill mixtures including other chemicals added to promote or improve the action of the cell of which the aluminous metal electrode is a part. For instance, good results areobtained when the mercury compound is added, in accordance with the principles of this invention, to an alkaline mixture containing inorganic halide such as that described by R. H. Brown in his copending application, Serial No. 693,593, filed August 28, 1946. In such case, however, alkalinity is not necessary to efiicient results, and excellent cell operation has been achieved using a backfill mixture containing 1 to 30 percent by weight of inorganic halide and an amount of mercury salt, the balance being a carrier such as earth or other inactive material of the type above indicated.

In some cases the effectiveness of the mercury compounds, or their utility, is improved by applying the compounds directly to the surface of the aluminous metal anode using the compound in mixture with some substance which will promote adherence of the mercury compound to the anode surface. The coating thus formed, which may if desired include-other substances, inert or usefully active to promote cathodic protection should contain at least 0.901 percent by coating weight of the mercury compound. The use of such coatings on the anode surface does not preclude the use of mercury compound in the backfill or other mass with which the anode is eventually 'sur- 45 rounded.

Fig. 3 is a cross sectional View of the anode on 60 line 33 of Fig. 2. 7

Referring to Fig. 1, a hole 2 is provided in soil l to receive the aluminous anode 4 and the surrounding backfill 3 containing a mercury-containing compound capable of yielding mercury in 65 contact with the buried anode. In a preferred embodiment of the invention the backfill 3 may also contain other chemicals such as alkaline materials and an inorganic halide to promote or which contains the mercury compound and the backfill 1 which does not contain such a compound. If desired, the mercur compound may be included, in the baokfill as in the installation shown in Fig. 1. The shape of the anode 4 and the surrounding coating 8 are more clearly seen in the cross'sectional view of Fig. 3.

Of themercury compounds I prefer mercurous chloride, the preference being based on practical considerations, such as availability, cost and relative insolubility under the conditions usually obtaining in cathodic protection installations.

The advantages secured by the practice of this invention are largely those of efiiciency and stead operation. Surrounded by backfills, or mixtures, containing mercury compound, the aluminous metal anode operates to steadily produce, in the galvanic cell and under installation conditions, a steady output of current at relatively high efficiencies. In practice I have observed efilciencies as high as 90 percent when mixtures embodying mercury compounds are used. In the case of one installation where various aluminous metal electrodes were installed in various types of earth for the purpose of protecting a pipe line the current output obtained was three to four times as large as obtained with conventional zinc electrodes and this output was obtained at relatively high efficiency.

Relatively efiicient results in cathodic protection installations will be achieved by the use of my invention, regardless of the specific compo-' sition of the aluminous metal electrode or the specific type of mixture or backfill used to contact or surround the same. Generally, some alu-l.

minum alloys give better results as aluminous metal anodes than do others but the advantages of my invention in increasing efiiciency and insuring steady cell operation will be secured, regardless of the aluminous metal anodes used, although a cell using such an anode of one specific composition will, as is known, have better overall characteristics than a cell using an aluminous metal anode of other composition. Likewise the advantages and benefits of this invention will be secured when the mixture and the aluminous metal anode are preformed, into a unitar package and installed as such. An example of such a package is'described in the copending application of R. B. Mears, Serial No. 705,508 filed October 25, 1946. If desired an aluminous metal anode may be coated with a mixture containing a mercury compound prior to installation, whether the electrode is used separately or as a part of a unitary package. I have found, for example, that improved aluminous metal anode operation is obtained by coating the anode with a mixturecontaining mercurous chloride and a protein base or a water paint or a resin emulsion paint, examples of which are known and described in standard works such'as, for instance, Protective and Decorative Coatings, volume III, published by John Wiley 8; Sons, Inc., New York, 1943, pages 470 and 484, prepared under the editorship of Joseph J. Mattiello. The invention is not, therefore, limited in usefulness to a specific aluminous metal electrode or'to a particular form'of cathodic protection system or mixture or backfill, except as indicated in the appended claims.

improve the action of the cell. The anode 4 is Having thus described my invention, I claim:

connected by wire 5 to an underground iron pipe 6.

The cathodic protection system illustrated in Fig. 2 is similar to that in Fig. 1 in every respect 1. In a cathodic protection installation designed and operative to protect a metallic underground structure against corrosion, and comprising an underground aluminous metal electrode except for the adherent coating 8 on anode 4 separate from said structure, electrically connected to said structure and anodic thereto, the improvement consisting in a backfill in contact with said electrode, said backfill containing at least 0001 percent by weight of a mercury compound capable of yielding metallic mercury when in contact with said underground aluminous electrode.

2. In combination with a metallic underground structure, a separately buried aluminous metal electrode anodic to the metal of said structure and electrically connected thereto and a backfill containing at least 0.001 percent of mercury compound in contact with said electrode, said compound being capable of yielding metallic mercury when in contact with said buried aluminous electrode.

3. The method of improving the eiiiciency of an underground galvanic cell composed of a separately buried aluminous metal anode electrically connected to a separately buried metallic cathode which comprises maintaining in contact with said anode a material containing at least 0.001 percent by weight of mercury compound capable of yielding metallic mercury when in contact with said buried aluminous electrode.

4. An anode for use in a cathodic protection installation said anode being formed of a body of aluminous metal the surface of which bears a dry coating containing mercury compound capable of yielding metallic mercury when in contact with said aluminous body in a cathodic protection installation.

5. In a cathodic protection installation designed and operative to protect a metallic underground structure against corrosion and including an underground aluminous metal electrode separate from said structure, electrically connected to said structure and anodic thereto, the improvement consisting in an alkaline backfill in contact with said electrode, said backfill containing at least 0.001 percent by weight of mercury compound capable of yielding metallic mercury when in contact with said underground aluminous electrode.

6. A unitary package for use in cathodic protection of underground metallic structures comprising an aluminous metal electrode in contact with a dry mixture containing at least 0.001 percent by weight of mercury compound capable of yielding metallic mercury when in contact with said aluminous electrode in a cathodic protection installation.

7. In a cathodic protection installation designed and operative to protect a metallic underground structure against corrosion and comprising an underground aluminous metal electrode separate from said structure, electrically connected to said structure and anodic thereto, the improvement consisting in the fact that the surface of said electrode is covered, at least in part, with a mercury compound capable of yielding metallic mercury when in contact with said underground aluminous electrode.

8. In combination with a metallic underground structure, a separately buried aluminous metal electrode anodic to the metal of said structure and bearing on its surface a mercury compound capable of yielding metallic mercury when in contact with said buried aluminous electrode.

9. In combination with a metallic underground structure, a separately buried aluminous metal electrode anodic to the said structure and electrically connected thereto and a backfill containing at least 0.001 per cent of mercury compound in contact with said electrode, said compound being capable of yielding metallic mercury when in contact with said buried aluminous electrode, and the ampere output per hour of said electrode being greater than the ampere output per hour of the same electrode in the described combination with said structure but not in contact with a backfill containing said mercury compound.

RAYMOND B. HOXENG.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Country Date Great Britain Oct. 31, 1935 Number OTHER REFERENCES 

1. IN A CATHODIC PROTECTION INSTALLATION DESIGNED AND OPERATIVE TO PROTECT A METALLIC UNDERGROUND STRUCTURE AGAINST CORROSION, AND COMPRISING AN UNDERGROUND ALUMINOUS METAL ELECTRODE SEPARATE FROM SAID STRUCTURE, ELECTRICALLY CONNECTED TO SAID STRUCTURE AND ANODIC THERETO, THE IMPROVEMENT CONSISTING IN A BACKFILL IN CONTACT 